Vehicle occupant detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and how forcefully, to deploy the restraint. For example, it is useful to know the seated weight of the occupant, and whether the detected weight is due to a normally seated child or adult, or a cinched booster seat or infant carrier. Additionally, the detection system must be capable of accurately providing the required occupant information throughout the expected life of the vehicle.
A popular and cost-effective way of providing the above-mentioned occupant data is to install a fluid-filled elastomeric bladder in or under the seat cushion, and to measure the fluid pressure in the bladder. See for example, the U.S. Pat. Nos. 5,987,370; 6,101,436; 6,246,936 and 6,490,936, assigned to the assignee of the present invention, and incorporated herein by reference. The measured pressure provides an indication of occupant weight, and the sensitivity of the bladder to occupant weight in different areas of the seat can be tailored to effectively distinguish between different types of occupants. For example, the bladder sensitivity can be minimized in areas of the seat normally engaged by an infant or booster seat so that the measured pressure for an infant or booster seat will be less than, say, a 5th percentile adult female occupant. In other words, the bladder geometry can be designed to result in a weight separation between occupants for whom deployment should be enabled and occupants for whom deployment should be disabled or reduced in force. See, for example, the  aforementioned U.S. Pat. No. 6,101,436, where bladder sensitivity is tailored by selectively welding the top and bottom layers of the bladder to form a pattern or array of flow-through cells or fluid-free pockets. However, the use of bladder geometry features for sensitivity tuning can be significantly restricted when a rigid interface panel or board is installed between the bladder and seat cushion. Interface panels are used to provide a controlled interface between the seat cushion and the bladder that limits the system sensitivity to seat foam variations caused by manufacturing irregularities, temperature and aging, and protects the bladder from puncture due to sharp objects coming into contact with the cushion. Interface panels can also be used between the bladder and the seat frame for similar reasons. See, for example, the aforementioned U.S. Pat. No. 6,490,936. In any event, such interface panels tend to evenly distribute the occupant weight over the bladder, masking the sensitivity variations that would otherwise occur due to bladder geometry features. Accordingly, what is needed is an interface panel for a seat bladder occupant weight estimation system that will protect the bladder and limit the system sensitivity to seat foam and suspension variations, without preventing the use of bladder geometry features for sensitivity control.